Optical device for biometric capture by contact and system using said device

Abstract

An optical device for biometric sensing by contact, comprising: an optical element ( 2 ) having a face ( 3 ) constituting a surface for apposition of a body part from which a biometric characteristic is to be sensed; a radiation source ( 6 ) for illuminating the face ( 3 ) of the optical element; and sensor means ( 9 ) for picking up the radiation coming from the face ( 3 ); the face ( 3 ) is coated in a thin layer defining a pattern and made of a material such that in association with the material constituting the optical element, the layer is transparent in the presence of radiation emitted by the radiation source ( 6 ) when a body part is placed on the face ( 3 ) and is significantly less transparent in the presence of external parasitic radiation ( 13 ) that is inclined relative to the face ( 3 ); whereby the image received by the sensor means can be distinguished depending on whether it is real or latent.

1. An optical device for biometric sensing by contact, the device comprising:
 an optical element having a face that constitutes at least in part a surface for apposition of a body part from which it is desired to sense a biometric characteristic; 
 an electromagnetic radiation source associated with said optical element to illuminate said face through the optical element with electromagnetic radiation substantially perpendicular to said face; and 
 sensor means suitable for picking up reflected radiation coming from said face of the optical element; 
 wherein said face of the optical element is coated with a thin layer defining a predetermined repeating pattern and made of a material such that, in relation with the material constituting the optical element, said thin layer defining said predetermined pattern is transparent to the electromagnetic radiation emitted by the radiation source when a body part is placed on said face of the optical element and is significantly less transparent for an interfering external electromagnetic radiation that is inclined relative to said face of the optical element and without any body part being apposed on said surface of the optical element, 
 whereby the image received by the sensor means can be discriminated as to whether it constitutes a real image or a latent image. 
 
   
   
     2. A device according to  claim 1 , wherein said thin layer is deposited on the face of the optical element as extra thickness in said predetermined pattern. 
   
   
     3. A device according to  claim 1 , wherein said thin layer is deposited continuously on the face of the optical element and has a transmission index that varies so as to provide said predetermined pattern. 
   
   
     4. A device according to  claim 1 , wherein said thin layer is deposited directly on said face of the optical element. 
   
   
     5. A device according to  claim 1 , wherein said thin layer is formed on a continuous transparent film and wherein said film is deposited on said face of the optical element. 
   
   
     6. A device according to  claim 1 , wherein said optical element is a prism having a base which is said face. 
   
   
     7. A device according to  claim 1 , wherein the material constituting the optical element is glass. 
   
   
     8. A device according to  claim 1 , wherein the material constituting said thin layer is ITO. 
   
   
     9. A device according to  claim 1 , wherein it is arranged to sense fingerprints. 
   
   
     10. An installation for biometric sensing by contact, comprising:
 at least one optical device for biometric sensing by contact in accordance with  claim 1 ; and 
 discrimination means comprising:
 memory means for storing an image of said predetermined pattern formed by the thin layer; 
 detector means for detecting, in an image received by the sensor means, the presence of the image of said predetermined pattern in superposition on a fingerprint image; and 
 a gate connected to said detector means and to said sensor means respectively, for rejecting as a latent image an image received by the sensor that is formed by the image of the predetermined pattern superposed on a fingerprint image.